In March 2008, the Justice Department made an extraordinary request: It asked a judge for permission to record secretly the phone conversations of Raj Rajaratnam, a billionaire hedge fund manager.

The request, which was granted, was the first time the government had asked for a wiretap to investigate insider trading. Federal agents eavesdropped on Mr. Rajaratnam for nine months, leading to his indictment — along with charges against 22 others — and the biggest insider trading case in a generation.

On Thursday, lawyers for Mr. Rajaratnam, who is serving an 11-year prison term after being found guilty at trial, will ask a federal appeals court to reverse his conviction. They contend that the government improperly obtained a wiretap in violation of Mr. Rajaratnam’s constitutional privacy rights and federal laws governing electronic surveillance.

Such a ruling is considered a long shot, but a reversal would have broad implications. Not only would it upend Mr. Rajaratnam’s conviction but also affect the prosecution of Rajat K. Gupta, the former Goldman Sachs director who was convicted of leaking boardroom secrets to Mr. Rajaratnam. Mr. Gupta is scheduled to be sentenced on Wednesday.

A decision curbing the use of wiretaps would also affect the government’s ability to police Wall Street trading floors, as insider trading cases and other securities fraud crimes are notoriously difficult to build without direct evidence like incriminating telephone conversations.

“Wiretaps traditionally have been used in narcotics and organized crime cases,” said Harlan J. Protass, a criminal defense lawyer in New York who is not involved in the Rajaratnam case. “Their use today in insider trading investigations indicates that the government thinks there may be no bounds to the types of white-collar cases in which they can be used.”

More broadly, Mr. Rajaratnam’s appeal is being closely watched for its effect on the privacy protections of defendants regarding wiretap use. Three parties have filed “friend-of-the-court” briefs siding with Mr. Rajaratnam. Eight former federal judges warned that allowing the court’s ruling to stand “would pose a grave threat to the integrity of the warrant process.” A group of defense lawyers said that upholding the use of wiretaps in this case would “eviscerate the integrity of the criminal justice system.”

To safeguard privacy protections, federal law permits the government’s use of wiretaps only under narrowly prescribed conditions. Among the conditions are that a judge, before authorizing a wiretap, must find that conventional investigative techniques have been tried and failed. Mr. Rajaratnam’s lawyers said the government misled the judge who authorized the wiretap, Gerard E. Lynch, in this regard.

They say that the government omitted that the Securities and Exchange Commission had already been building its case against Mr. Rajaratnam for more than a year using typical investigative means like interviewing witnesses and reviewing trading records. Had the judge known about the S.E.C.’s investigation, he would not have allowed the government to use a wiretap, Mr. Rajaratnam’s lawyers argue.

Before Mr. Rajaratnam’s trial, the presiding judge, Richard J. Holwell, held a four-day hearing on the legality of the wiretaps. Judge Holwell criticized the government, calling its decision to leave out information about its more conventional investigation a “glaring omission” that demonstrated “a reckless disregard for the truth.”

Nevertheless, Judge Holwell refused to suppress the wiretaps, in part, he said, because they were necessary to uncover Mr. Rajartanam’s insider trading scheme. “It appears that the S.E.C., and by inference the criminal authorities, had hit a wall of sorts,” Judge Holwell wrote.

On appeal, Mr. Rajaratnam lawyers argued that the government’s lack of candor should not be tolerated. They described the government’s wiretap application as full of “misleading assertions” and “outright falsity” that made it impossible for Judge Lynch to do his job.

“The government’s self-chosen reckless disregard of the truth and of the critical role of independent judicial review breached that trust and desolated the warrant’s basis,” wrote Mr. Rajaratnam’s lawyers at the law firm Akin Gump Strauss Hauer & Feld.

In their brief to the appeals court, federal prosecutors dispute that they acted with a “reckless disregard for the truth.” Instead, they argue that omitting details of the S.E.C.’s investigation was at most “an innocent mistake rising to the level of negligence.” In addition, they said that the S.E.C.’s inquiry failed to yield sufficient evidence for a criminal case, necessitating the use of a wiretap.

Once Judge Lynch signed off on the wiretap application, the government’s investigation into Mr. Rajaratnam accelerated. The wiretapping of Mr. Rajaratnam’s phone, along with the subsequent recording of his supposed accomplices, yielded about 2,400 conversations. In many of them, Mr. Rajaratnam could be heard exchanging confidential information about technology stocks like Google and Advanced Micro Devices.

Three years ago this month, federal authorities arrested Mr. Rajaratnam and charged him with orchestrating a seven-year insider trading conspiracy. The sprawling case has produced 23 arrests of traders and tipsters, many of them caught swapping secrets with Mr. Rajaratnam about publicly traded companies.

Among the thousands of calls were four that implicated Mr. Gupta, a former head of the consulting firm McKinsey & Company who served as a director at Goldman Sachs and Procter & Gamble. On one call in July 2008, the only wiretapped conversation between the two men, Mr. Gupta freely shared Goldman’s confidential board discussions with Mr. Rajaratnam. On another, Mr. Rajaratnam told a colleague at his hedge fund, the Galleon Group, “I heard yesterday from somebody who’s on the board of Goldman Sachs that they are going to lose $2 per share.”

Those conversations set off an investigation of Mr. Gupta. He was arrested in October 2011 and charged with leaking boardroom secrets about Goldman and P.& G. to Mr. Rajaratnam. A jury convicted him in May after a monthlong trial.

On Wednesday at Federal District Court in Manhattan, Judge Jed S. Rakoff will sentence Mr. Gupta. Federal prosecutors are seeking a prison term of up to 10 years. Mr. Gupta’s lawyers have asked Judge Rakoff for a nonprison sentence of probation and community service. One proposal by the defense would have Mr. Gupta living in Rwanda and working on global health issues.

Regardless of his sentence, Mr. Gupta plans to appeal. And because prosecutors used wiretap evidence in his trial, Mr. Gupta would benefit from a reversal of Mr. Rajaratnam’s conviction.

Yet a reversal would not affect the convictions of the defendants in the conspiracy who have pleaded guilty. As part of their pleas, those defendants waived their rights to an appeal.”

Douglas McNabb and other members of the U.S. law firm practice and write and/or report extensively on matters involving Federal Criminal Defense, INTERPOL Red Notice Removal, International Extradition Defense, OFAC SDN Sanctions Removal, International Criminal Court Defense, and US Seizure of Non-Resident, Foreign-Owned Assets. Because we have experience dealing with INTERPOL, our firm understands the inter-relationship that INTERPOL’s “Red Notice” brings to this equation.

The author of this blog is Douglas C. McNabb. Please feel free to contact him directly at mcnabb@mcnabbassociates.com or at one of the offices listed above.